This invention relates generally to a method and apparatus for capturing coating debris during removal of layered material from a substrate, and more specifically to a laser ablation nozzle for removing the coating from the ends of a photoreceptor preferably while capturing the resulting coating debris, thereby minimizing redeposition of the coating material on the photoreceptor and ensuring a safe work environment. The phrase coating debris includes particulate matter and fumes resulting from the removal process.
In electrophotography, and particularly in xerographic copying machines, coated substrates such as photoreceptor belts or cylindrical photoreceptor drums are common. Photoreceptor embodiments include at least one coating of photosensitive material, which can be formed on the photoreceptor by known techniques such as immersion or dip coating.
The peripheral ends of a coated photoreceptor are used to engage with flanges in a copier's drive mechanism and/or to support a developer housing. If the developer housing rides on the coated area at one end of the drum, the coating material is rubbed off and contaminates various components in the machine such as the cleaning system and any optical exposure systems employed in the machine. Also, the coating can interfere with devices that are designed to electrically ground the drum by merely riding on the outer surface at one end of the drum. Thus, both the outer and inner peripheral ends of a photoreceptor must be free of coating material.
Conventionally, the ends of a photoreceptor are masked before coating to prevent them from being coated. In dip coating, the upper end of the photoreceptor drum might be kept free of coating material by orienting the drum vertically and dipping the drum into a bath of coating material to a predetermined depth. However, the coating formed over the lower end of the photoreceptor must still be removed, usually by mechanically wiping the lower end and/or by applying solvents to it. Chemical treatments can cause solvent droplets or vapor to contact the coating in regions that are not intended to be removed, reducing the quality of the resulting photoreceptor. In addition, the initial cost of the solvent, and cost of solvent recovery can be very high. Moreover, where the coatings may contain different layers of different materials, different solvents may be required to remove different layers. This adds to the complexity of removal of photoconductive coatings with the aid of a solvent because each layer has to be separately treated with different solvent. Furthermore, organic solvents have a limited useful life and can be hazardous to work with. Mechanical techniques for removing coatings are cumbersome, inefficient, and often produce photoreceptors of unacceptable quality.
Japanese Publication No. 3-144,458 discloses a process that attempts to remove coatings from the ends of a photoreceptor without mechanical or chemical treatment. A laser beam from an yttrium-aluminum-garnet laser is irradiated at the end portions of a photoreceptor drum to burn or sublimate the photoreceptor coating.
Japanese Publication No. 3-194,131 discloses a similar process in which laser energy is directed at the ends of a photoreceptor in an effort to completely remove the coating.
U.S. Pat. No. 4,877,644 to Wu et al., issued Oct. 31, 1989--A method for the selective plating of a metal substrate on which a thin polymeric resist is first applied, followed by the selective removal of the resist to expose portions of the substrate to plating, and plating. More particularly, the method includes the steps of selecting a laser wavelength which couples well to the metal substrate, choosing a polymer based plating resist having a low optical coefficient of absorption at the wavelength, curing the resist, subjecting selective areas of the resist to a single excimer laser shot, having a short wavelength, to cause ablative removal of the resist over selective areas of the substrate, and subjecting the exposed portions of the substrate to metal plating.
U.S. Pat. No. 4,671,848 to Miller et al., issued Jun. 9, 1987--a method for removing a dielectric coating from a conducting material is disclosed, wherein a high energy radiation source, such as a laser source, is focused in a region having a predefined relationship with the coating of the conducting material. The focused radiation results in a plasma or ionized region being formed. The coating in the vicinity of the plasma region is removed. The region of the focusing of the radiation is varied spatially to remove the dielectric coating in a pre-selected region of the conducting material. According to one embodiment, the radiation is focused in a region spatially removed from the conducting material in order that the direct radiation does not directly impact the conducting material.
U.S. Pat. No. 5,164,567 to Gettemy, issued Nov. 17, 1992--A method of cutting with a laser beam is disclosed where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes.
LIFT-OFF STENCIL CREATED BY LASER ABLATION, IBM Technical Disclosure Bulletin, Vol. 28, No. 5, October 1985, page 2034--a system is disclosed for ablating polymeric materials to create holes, vias, or lift-off stencils having a finite taper.
Copending patent application U.S. Ser. No. 08/178,166, filed Jan. 6, 1994, the disclosure of which is totally incorporated by reference, discloses a laser ablation system employing an annular compressed fluid curtain to assist in removal of a coating. There is also disclosed an annular nozzle coaxial with a coated substrate to supply a high pressure annular curtain of compressed fluid at an angle to the coated cylinder to assist in removal of a coating.
Copending patent application U.S. Ser. No. 08/071,087, filed Jun. 4, 1993, which is totally incorporated by reference, discloses a process for treating a predetermined portion of a coating on a photoreceptor to remove at least part of the coating. The process involves directing a source of high energy irradiation at the coating in the presence of at least one fluid medium to remove at least part of the coating from the predetermined portion of the coating. The source of high energy irradiation is preferably a laser beam, ultrasonic energy, or a source of high intensity heat. The at least one fluid medium is preferably at least one gas jet, liquid jet or a liquid solvent. There are disclosed a fluid coaxial jet and a fluid cross-jet.
Although laser treatment processes are intended to completely remove coatings, it has been found that many materials commonly used in photoreceptor coatings are melted, rather than vaporized, by these processes. The molten coating subsequently hardens and is removed as a dusty debris by associated fluid jets.